In order to help set the dark mood of the novel Browne incorporated a technique called 'dark plate' on ten of the illustrations. The dark plate technique involved using a ruling-machine (operated by an assistant) which cut a close-spaced criss-cross pattern of lines into the plate, thus creating an overall dark cast on the resulting print.

The illustration depicting Toms-all-Alone's, the slum that is home to the crossing-sweeper, Jo, is perhaps the most striking example of the dark plate technique.